Submonolayer Rare Earth Silicide Thin Films on the Si(111) Surface

Rare earth induced silicide phases of submonolayer height and 5 × 2 periodicity on the Si(111) surface are investigated by density functional theory and ab initio thermodynamics. The most stable silicide thin film consists of alternating Si Seiwatz and honeycomb chains aligned along the [1\(\overline{1}\) 0] direction, with rare earth atoms in between. This thermodynamically favored model is characterized by a minor band gap reduction compared to bulk Si and explains nicely the measured scanning tunneling microscopy images.